Prior methods of producing a metal catalyst carrier by forming a porous metal oxide coating over the surface of stainless steel include:
(a) wash-coating, in which a particular stainless steel (Fe--Cr--Al series) is subjected to surface oxidation to form an Al.sub.2 O.sub.3 coat thereover and is dipped (by the dipcoat method) in a slurry prepared by blending and stirring an active alumina powder, a wash-coat binder, aluminum nitrate, and water so that the coated stainless steel is additionally coated with the slurry (see Nikkei New Material, Nov. 28, 1988, page 25);
(b) dipping a metal network structure as a metal carrier in a benzene solution of a metal alkoxide and then in water and, thereafter, firing the thus-dipped structure; and
(c) coating a paste of a metal oxide over a metal carrier, followed by drying (see Japanese Patent Application Laid-Open No. 54-122690).
Since the wash-coat method uses a metal oxide powder having large grains (mean grain size of from 0.01 .mu.m to 30 .mu.m), the adhesion between the surface of the stainless steel and the metal oxide coating is limited; and, in addition, the shape of the stainless steel to be used therein is limited to mesh, honeycomb, and plate shapes. Thus, the method is not always satisfactory. A further drawback is that the stainless steel to be used for applying the active alumina powder is limited to the Fe--Cr--Al series.
In accordance with the method described in Japanese Patent Application Laid-Open No. 54-122690, control of the pore diameter of the metal oxide grains is difficult, and the carrier obtained could hardly have a high dispersibility of noble metal catalysts therewith.